The present ongoing project involves analysis of data gathered from 1,000 intact families and comparisons with the longitudinal behavioral ratings and Q-sort data at adolescence and adulthood from the Oakland Growth and Berkeley Guidance Studies, University of California, Berkeley. Personal styles throughout the course of development antecedent to the acquisition of mates and offspring are examined to determine causal personality factors in subsequent fertility rates. Analysis via family structural factors is the focus (sex, sex of sibling, family size, ordinal position, age-spacing). Where family size has demonstrable impact on adult personality and fertility, mothers appear prime determiners of offspring numbers, fathers appear prime determiners of spouse selection. Personological qualities of high and low fertile mothers emphasize ego-intactness and adjustment for mothers of large families, while mothers who subsequently have few offspring are characterized in childhood and adolescence as immature, inpulsive, ill- socialized, with somewhat brittle egos. Personal qualities of fathers of large and small families suggest fewer but parallel qualities contingent upon family size.